Compression??????

[RAM318]

HOW CAN I TELL WHAT MY COMPRESSION IS ? I JUST HAD A 75 360 REBUILT AND ASKED FOR 9:1 PISTONS TO BE INSTALLED . IS THERE A WAY TO CHECK IT? NO SPECIAL HEAD WORK WAS DONE ,JUST A 3 ANGLE VALVE JOB. THANKS

[69Dodgedart360]

find out your piston/deck height (how far below the deck the piston is at TDC), cc's of your heads, and the head gasket thickness. take all this information to the compression ratio calculator in the mathematics section of www.prestage.com
and plug it in. it will tell you the compression ratio.

[Glen440]

Wow thats a usefull site. Checked the comp of my last engine.
Woohoo a whopping 7.8-1 hehehe. I thought it was 8-1.

[DAVE JONES]

Ram, unless you have the specs like these guys said, you wont be able to figure out the CR. You may want to go back to the shop where they did the work and after you ask them what CR they set it up for, then ask them for the actual specs that they used and write it down. Then plug them into the calculator and check. There is alot of misconception when ordering pistons since alot of people think that the end CR will be what piston they ordered but there are other main variables that play a major role.....good luck doc. Hopefully you will get the info and answers you want.

Hey Glen, you didnt tell us when the blower is going on.

[Glen440]

I wish it were a blower motor. It was just a cheap 400 I bought.
You need binoculers to see the pistons, thats how far down the hole they are(.134"). Couldn't go wrong for $300 for a complete fresh never run engine. The cheap engines never gave me problems. Once you put some money in them problems start. The ones you wish would blow up won't.

[Jims451]

If the engine is assembled and on an engine stand you can "cc" the assembled engine through the spark plug hole.

First you should remove the rocker arms for the #1 cylinder so the valves are alaways closed, or just be sure your at TDC when ignition takes place.
#2 Rotate the engine on the engine stand so the sparkplug hole is at the highest point so air can escape out the spark plug hole.
#3 Bring #1 piston to TDC. The zero mark on the timming chain cover should be at zero, and you can sort of verify TDC by having a wire or scredriver through the spark plug hole you can "Feel" the piston top reach TDC as you rotate the engine.
#4 With the piston at TDC, Measure how much oil it takes to fill the chamber/cylinder above the piston. This will give you the CC's above the piston including the head volume, gasket volume, and deck height volume.

Once your done, make sure to dump the oil back out of the cylinder and spin the engine over a few times with the spark plug out to make sure you don't hydraulic the engine.
If you removed the rocker arms, put them back also.
#5 You can either calculate the piston swept volume if you know the bore and stroke, or you can lower the piston to BDC (make sure valves are still closed) and "cc" the cylinder again by measuring how much oil it takes to fill the cylinder again.
#6 Add the piston swept volume calculated or measured in #5 and add it to the volume from #4, then divide the total by #4 to get the compression ratio.

[RAM318]

thanks everyone for the info. i might be up the creek here. the motors already in and running. im going back to the shop that built the motor and see if they know the cc of heads and deck depth. thanks again ram318